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Published December 15, 1997 | Published
Journal Article Open

Observed OH and HO_2 in the upper troposphere suggest a major source from convective injection of peroxides


ER-2 aircraft observations of OH and HO_2 concentrations in the upper troposphere during the NASA/STRAT campaign are interpreted using a photochemical model constrained by local observations of O_3, H_2O, NO, CO, hydrocarbons, albedo and overhead ozone column. We find that the reaction Q(^(1)D) + H_2O is minor compared to acetone photolysis as a primary source of HO_x (= OH + peroxy radicals) in the upper troposphere. Calculations using a diel steady state model agree with observed HO_x concentrations in the lower stratosphere and, for some flights, in the upper troposphere. However, for other flights in the upper troposphere, the steady state model underestimates observations by a factor of 2 or more. These model underestimates are found to be related to a recent (< 1 week) convective origin of the air. By conducting time-dependent model calculations along air trajectories determined for the STRAT flights, we show that convective injection of CH_3OOH and H_2O_2 from the boundary layer to the upper troposphere could resolve the discrepancy. These injections of HO_x reservoirs cause large HO_x increases in the tropical upper troposphere for over a week downwind of the convective activity. We propose that this mechanism provides a major source of HO_x in the upper troposphere. Simultaneous measurements of peroxides, formaldehyde and acetone along with OH and HO_2 are needed to test our hypothesis.

Additional Information

© 1997 American Geophysical Union. Received June 30, 1997; accepted September 16, 1997. Paper number 97GL03004. This work was supported by the National Aeronautics and Space Administration (NASA-NAG5-2688; NASA-NAG2-1100) and the National Science Foundation (NSF-ATM-9612282). We thank the ground crew and pilots of the ER-2 for their efforts in obtaining the data set. STRAT was sponsored by NASA's Upper Atmosphere Research Program, the Atmospheric Effects of Aviation Project, and the Atmospheric Chemistry Modeling and Analysis Program. The project scientists for STRAT were Paul Newman, NASA Goddard, and Steven Wofsy, Harvard University.

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